As integration density of integrated circuit devices increases, use of a dielectric layer having a high dielectric constant may be used to obtain high capacitance in a small space. The high dielectric constant material may be Ta2O5, TiO2, Al2O3, Y2O3, ZrO2, HfO2, BaTiO3, or SrTiO3.
Although these oxide layers have a relatively high dielectric constant, they may react with polysilicon, which is a material commonly used as a lower electrode in conventional capacitors. For example, polysilicon may be oxidized by reacting with a tantalum oxide layer during a process of forming the tantalum oxide layer or during a thermal treatment process after formation of the tantalum oxide layer. To reduce oxidation, a nitride layer may be interposed between the tantalum oxide layer and the polysilicon and used as a barrier layer against diffusion of oxygen.
Another approach to reducing oxidation involves forming a lower electrode of a material that is relatively difficult to oxidize. For example, a noble metal, such as Pt, Ru, Ir or a conductive metal nitride, such as TiN may be used. FIG. 1 illustrates a Ru layer 110 that is formed on a silicon substrate 100 and thermally treated in an ozone (O3) atmosphere at 250° C. As shown in FIG. 1, columnar crystal phases 120 exist on the surface of the Ru layer 110. These columnar crystal phases 120 are RuO2, which is formed by oxidization of the Ru layer 110 due to ozone. These RuO2 crystal phases 120 may inhibit formation of the dielectric layer (e.g., a tantalum oxide layer) and also deteriorate the properties of the capacitor by reducing the contact area between the Ru layer 110 and the dielectric layer. In particular, when the dielectric layer is formed on a substrate having a cylindrical opening, such as, for example, an opening for a cylindrical capacitor, the dielectric layer may not be formed on lower portions of the opening. As a result, step coverage of the dielectric layer may deteriorate.